Plasma processing apparatuses are widely used in manufacturing process of integrated circuit (IC) or photovoltaic cell with the development of plasma technology. Research on plasma processing apparatuses which are suitable for etch, deposition or some other process is very important to the development of the manufacturing process of IC or photovoltaic cell.
Currently, parallel plate Capacitively Coupled Plasma (CCP) processing apparatuses are often used in the industry of IC or photovoltaic cell. The principle of generating plasma by such apparatuses is very simple: generally one electrode plate is applied with RF power, the other electrode plate is grounded, and the generation and maintain of CCP mainly rely on the RF electrical field between two electrode plates.
For example, FIG. 1 shows a parallel plate capacitively coupled Plasma Enhanced Chemical Vapor Deposition (PECVD) apparatus which is commonly used in practice. Such PECVD apparatus includes: a reaction chamber 80, a power supply 10 and a match coupling device (not shown) outside the reaction chamber 80, an upper electrode 20 which locates in the reaction chamber 80 and is connected with the power supply 10, a grounded electrode 30 inside the reaction chamber 80. Densely distributed gas inlet holes 40 are provided on the upper electrode plate 20; a gas outlet port 50 is provided bottom of the reaction chamber 80; and a substrate to be processed locates on the grounded electrode 30.
During the operation of the PECVD apparatus, under a suitable vacuum condition, process gas is introduced into the reaction chamber 80 through the gas inlet holes 40; the process gas between the upper electrode 20 and the grounded electrode 30 is excited by the power supply to generate plasma 60; the plasma 60 reacts with the substrate; and product of the reaction deposits on the substrate so as to form a film, while waste gas produced by such reaction is drawn out via the gas outlet port 50.
Currently, however, requirement of the industry of IC or photovoltaic cell with respect to productivity is highly increased, that is, under the condition of ensuring the quality of the etch process or the deposit process, more products need to be produced within the same time interval. In order to meet such requirement, apparatus manufacturers increase the size of plasma apparatuses continuously, so that a larger wafer can be processed in one process to improve the productivity of apparatuses.
Although the commonly used parallel plate CCP apparatuses can produce relatively uniform plasma compared to other plasma apparatuses (e.g. an electron cyclotron resonance plasma processing apparatus and an inductively coupled plasma processing apparatus). However, with the increase of the size of the reaction chamber and the increase of the area of the electrode plates, especially when the frequency of the power supply is comparatively higher, a standing wave effect and an edge effect will occur in such parallel plate CCP apparatus. The standing wave effect and the edge effect have great influence on the uniformity of the generated plasma and usually cause a phenomenon that the plasma at the center of the electrode plate has a higher density and the plasma at the edge has a lower density, so that the uniformity of the result of plasma processing process is thus influenced.